Ion source



uly 10, 1956 G. A. BOUTRY ET AL 2,754,442

ION SOURCE Filed March 19, 1955 J INVENTORE') GEORGES AIBERT BOUTRY GECRGES ADOLP HE VINCENT PIETRI BY Z W AGENT United States Patent ION SOURCE Georges Albert Boutry, Villecresne, and Georges Adolphe Vincent Pietri, Asnieres-Seine, France, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application March 19, 1953, Serial No. 343,372 Claims priority, application France March 21, 1952 12 Claims. (Cl. 313-63) This invention relates to an ion source in which ions are produced on a heated anode and are then accelerated.

In a known device of the above-mentioned kind a neutral gas flow is directed through a fine aperture to the anode. The continuous supply of gas makes it necessary to connect the device to a pump system. In addition the tendency of a gas to ionise on a glowing anode is comparatively low so that the ions produced are enclosed between neutral atoms or molecules and this may upset the movement which is due to the action of electric or magnetic fields. The object of the invention is therefore to provide an ion source of greater efiiciency than the known ion sources while avoiding the need for a pump.

According to the invention, the ions produced on a heated anode of an ion source are constituted by ions of a readily volatilising metal and the material of the anode is chosen with respect to the said metal so that at the operating temperature of the device the ratio between the total number of ions produced and the total number of atoms volatilised is substantially equal to unity, the ions collected on the collecting electrode being held there.

The ratio between the number of ions produced (m) and the total number of atoms vaporized per unit surface (Fla) is given by the formula where A is a factor, k is the Boltzmann constant, W the work function of the electrons emerging from the anode material concerned at the absolute temperature T and W1 designates the first ionisation work of the metal volatilising from the anode. Obviously, the higher positive the value of Ws-W1 the greater is the ratio Ill/Ha. The amount WS-Wl is positive for an anode made of platinum, the volatilising metal being cesium, rubidium, potassium, barium, sodium or lithium. The same remark applies to nickel or iron on the one hand and cesium, rubidium or potassium on the other. As an alternative the anode may otherwise be made of molybdenum, tungsten, or carbon. The alkali metal may be applied to the anode by directing a vapour flow on to the anode or by vaporising the metal from the anode itself through apertures or through a porous wall, the supply of readily vaporising metal not being necessarily at the same temperature as the anode surface itself.

The ions recombined on the collecting electrode may be condensed there in that the temperature of this electrode is very low or the electrode itself is provided with a layer which absorbs the metal concerned. If required, the other electrodes provided in the tube and the entire tube wall may also be provided with such an absorbing layer. If the metal vapour is held only by the low temperature of the collecting electrode and the supply of metal can be caused to assume a low temperature regeneration of the ion source may be efiected.

In order that the invention may be readily carried into 2,754,442 Patented July 10, 1956 effect, it will now be described with reference to the accompanying drawings in which:

Figs. 1 to 3, show by way of example three embodiments of an ion source according to the invention. Referring to Fig. 1, the envelope 1 of the ion source is diagrammatically shown. 2 designates a container for a supply of alkali metal 3 comprising an outflow spout 5 and provided with a heater 4. On the container 2 being heated a directed alkali vapour fiow flows from the spout 5 to an anode 6 which is provided with a heater 7. The flow of alkali metal vapour impingent on the anode 6 is converted with high efficiency into alkali ions and accelerated by means of an electrode 8 towards a collecting electrode 9 which is coated with an absorbing layer 10, such as lead oxide. The accelerating anode 8 and the collecting electrode 9 may be separated by a device in which the ions are used, such as a signal-retarding device, a pulse generator or a device in which use is made of nuclear energy. In principle provision may be made of several containers 2 for a variety of metals.

Referring to Fig. 2, the parts similar to Fig. 1 are designated by like references but the container 11 also acts as the anode due to the fact that adjacent the accelerating electrode 8 it is made of porous sintered metal. Referring to Fig. 3, the supply of alkali metal 3 is enclosed in a glass container 2 which slightly projects beyond the envelope 1. The container has sealed to it a metal chamber 12 the upper wall of which has an aperture 13 formed in it. The aperture 13 opens out into a chamber 14 the upper surface 16 of which constitutes the anode which has an aperture formed in it. A heater 15 is arranged to surround the chamber 14. The device comprises in addition an accelerating electrode 17, a device 19 for use of the ions and a collecting electrode 18. In this device the vapour pressure of the alkali metal is independent of the anode temperature and this may increase the ionisation efiiciency. In addition, regeneration of the tube may be effected by cooling the supply 3 and heating the tube 1 to bring about retro-vaporisation of alkali metal. A supply of alkali metal of 1 g. otherwise suflices to operate the tube for several thousand hours.

What is claimed is:

1. An ion device comprising a source of readily vola tilising metal, an anode positioned to receive the metal volatilized from said source, means for heating the anode at a given operating temperature to ionize said metal, said anode being constituted of a material at which the ratio of the total number of ions produced and the total number of metal atoms volatilised is substantially equal to unity, and a collecting electrode spaced from said anode and positioned to collect the ions emanating therefrom, said collecting electrode being adapted to retain the ions collected thereby.

2. An ion device comprising a source of readily volatilizing metal, an anode positioned to receive the metal volatilized from said source, means for heating the anode at a given operating temperature to ionize said metal, said anode being constituted of a material at which the ratio of the total number of ions produced and the total number of metal atoms volatilized is substantially equal to unity, a collecting electrode spaced from the anode and positioned to collect the ions emanating therefrom, and a coating of material capable of absorbing ions on said collecting electrode.

3. A device as claimed in claim 2 in which the absorbing material is lead oxide.

4. An ion device comprising a source of readily volatilizing metal selected from the group consisting of cesium, rubidium, potassium, barium, sodium and lithium, an anode positioned to receive the metal volatilized from said source, means for heating the anode at a given operating temperature to ionize said metal, said anode being constituted of platinum, and a collecting electrode spaced from the anode and positioned to collect the ions emanating therefrom.

5. A device as claimed in claim 1 wherein the-ano de material is selected from the group consisting of nickel and iron, and the metal is selected from the group -consisting of cesium, nlbidium and potassium. 1

6. A device as claimed in claim 1 wherein the anode material is selected from the group consisting of molybdenum, tungsten and carbon.

7. An ion device comprising a housing, a supply chamber disposed on the bottom of said housing, a supply of a readily volatilising metal disposed in said chamber, an anode disposed Within said housing and communicating with said chamber, said anode having a small aperture therein, heating means disposed adjacent said anode for heating said anode to an operating temperature to ionize metal volatilized thereon, said supply chamber being at a temperature difierent from said operating temperature of said anode, an accelerating electrode disposed.

in front of said anode for removing ions produced thereby, and a collector electrode spaced from said accelerating electrode on the side thereof remote from said anode to collect the ions emanating therefrom, said collecting electrode being arranged to retain the ions collected thereby, said anode being constituted of a material at which the ratio of the total number of ions produced and the total number of metal ions volatilized is substantially equal to unity.

8. A device as claimed in claim 7 wherein the collecting electrode is coated with a layer of material capable of absorbing and retaining ions.

9. A device as claimed in claim 8 in which the inner wall of the housing and the other electrodes are provided with a coating of material capable of absorbing and re taining ions.

10. A device as claimed in claim 7 wherein the collecting electrode is maintained at a very low temperature relative to the anode in order to retain the ions.

11. An ion device comprising a supply chamber including an outlet, a supply of readily volatilisable metal disposed in said chamber, an anode plate spaced from and facing said outlet of' said chamber, means for heating the chamber to volatilise the metal and cause the same to flow toward the anode, means for heating the anode to convert the volatilised metal into ions, said anode being constituted of a material at which the ratio of the total number of ions produced and the total number of metal ions volatilised is substantially equal to unity, and a collecting electrode spaced from said anode, and positioned to collect the ions emanating therefrom,-said electrode being provided with a layer of a material capable of absorbing and retaining ions.

. 12. An ion device comprising a supply chamber, a supply of readily volatilisable metal disposed in said chamber, a wall of said chamber being porous and serving as an anode, means for heating the chamber to volatilise the metal and also ionize the latter, said anode being constituted of a material at which the ratio of the total number of ions produced and the total number of metal ions volatilized is' substantially equal to unity, and a collecting electrode spaced from said anode and positioned to collect the ions emanating therefrom, said electrode being prov vided with a layer of a material capable of absorbing and retaining ions.

References Cited in the file of this patent UNITED STATES PATENTS 1,931,254 Doering Oct. 17, 1933 2,078,112 Wologdin Apr. 20, 1937 2,281,638 Sukumlyn May 5, 1942 2,697,169 Emslie Dec. 14, 1954 

7. AN ION DEVICE COMPRISING A HOUSING, A SUPPLY CHAMBER DISPOSED ON THE BOTTOM OF SAID HOUSING, A SUPPLY OF A READILY VOLATILISING METAL DISPOSED IN SAID CHAMBER, AN ANODE DISPOSED WITHIN SAID HOUSING AND COMMUNICATING WITH SAID CHAMBER, SAID ANODE HAVING A SMALL APERTURE THEREIN, HEATING MEANS DISPOSED ADJACENT SAID ANODE FOR HEATING SAID ANODE TO AN OPERATING TEMPERATURE TO IONIZE METAL VOLATILIZED THEREON, SAID SUPPLY CHAMBER BEING AT A TEMPERATURE DIFFERENT FROM SAID OPERATING TEMPERATURE OF SAID ANODE, AN ACCELERATING ELECTRODE DISPOSED IN FRONT OF SAID ANODE FOR REMOVING IONS PRODUCED THEREBY, AND A COLLECTOR ELECTRODE SPACED FROM SAID ACCELERATING ELECTRODE ON THE SIDE THEREOF REMOTE FROM SAID ANODE TO COLLECT THE IONS EMANATING THEREFROM, SAID COLLECTING ELECTRODE BEING ARRANGED TO RETAIN THE IONS COLLECTED THEREBY, SAID ANODE BEING CONSTITUTED OF A MATERIAL AT WHICH THE RATIO OF THE TOTAL NUMBER OF IONS PRODUCED AND THE TOTAL NUMBER OF METAL IONS VOLATILIZED IS SUBSTANTIALLY EQUAL TO UNITY. 